194 J. H. ASHWORTH. 



size, being only 6 /j. to 7 p, long and 2 p. wide. The nematocysts of 

 Alcyonaria are all very small, as may be seen from the following table : 



Sarcophyton pauciflomm 1 



6 p — 7 m- long and 2 (j. wide (J. H. A. ) 



Alcyonium cligitatum - - 



li ^ ,, ,, 2^—3^ ,, (Hickson) 



Xenia Hicksoni- - • - 



8/* „ „ 2/A--3/C* ,, (J. H. A.) 



Heteroxenia Elizabcthce - 



9/tt ,, „ 2^/* ,, (J. H. A.) 



Clavularia viriclis - - - 



<V-10> ,, ,, 2^—3^ ,, (J. H. A.) 



Heliqpora ccerulea- - - 



9^. , (Moseley) 



Clavularia prolifera - - 



10 ac— 15 ^ „ (v. Koch) 



Spicules (PI. XX., Figs. 13—15; PI. XXL, Fig. 16).— The spicules, 

 the form of which was compared by Kblliker to that of red blood- 

 corpuscles, are rounded or oval discs, which are, however, sometimes 

 bilobed (Fig. 13). They are '012 mm. to "022 mm. long, "006 mm. to 

 •013 mm. broad, and "003 mm. to '005 mm. thick. 



Spicules are absent from the tentacles and pinnules of all the polyps 

 examined except one. In the latter a few small spicules (about 8 p to 

 12 n long) are present in the ectoderm of the tentacles, but only in the 

 proximal "4 mm. 



In the deeper part of the ectoderm, just below the point of attach- 

 ment of the tentacles, spicules are present in small numbers, while in 

 the middle and proximal portions of the body of the polyp they are 

 very numerous, a tangential section of the body-wall in this region 

 showing that the spicules form an almost complete layer in the deeper 

 part of the ectoderm. Spicules are numerous in the ectoderm of the 

 stem, and especially numerous in the angle of the Y-shaped piece 

 formed at the point of division of a stem. In the lowest parts of the 

 colony, i.e., in the portion attached to the rock, they are present in 

 enormous numbers, practically filling the entire mesoglcea in that 

 region. The largest examples of spicules are to be found in the basal 

 portion of the colony. (Those shown in Fig. 13 are from this region.) 

 The absence of spicules from the tentacles, pinnules, and from the 

 body of the polyp around the base of the tentacles is correlated with 

 the power of contractility, slight though it is, which is possessed by these 

 parts. The presence of an almost complete layer of spicules forming a 

 more or less rigid cylinder in the middle and proximal portions of the 

 body of the polyp and in the stem, together with the absence of muscle 



1 S. -pauciflorxim, TLhrenberg = Lobophytum pauciflorum, v. Marenzeller, 

 'Zool. Jahrb.,' i., 1886. 



